<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    var arr = [1,[[2,3],4],[5,6]];
    var flat = function* (a) {
      for(var i = 0; i < length; i++) {
        var item = a[i];
        if(typeof item !== 'number') {
          yield* falt(item)
        } else {
          yield item;
        }
      }
      
    }
    for(var f of flat(arr)) {
      console.log(f);
    }

    console.log('hello' + (yield));
    console.log('hello' + (yield 123));
  </script>
</body>
</html>